The present invention is directed generally to the control of undesirable odors typically generated by microbial activity in waste water systems. The present invention is particularly directed to the reduction of such undesirable odors in the immediate vicinity of wastewater lift stations, pumping stations, and other pretreatment facilities.
Modern wastewater collection systems, often referred to as sewage systems, are designed to capture and transport effluent from sources such as homes, schools, offices and factories to a common wastewater treatment facility. At the treatment facility, the wastewater is biologically and chemically treated so that the water can be released back into the environment with as little impact as possible. Treatment facilities are generally open to the atmosphere to promote aerobic microbial processes to biologically reduce the undesirable characteristics of the wastewater, and for that reason are typically situated in remote, thinly populated areas. The collection system leading to the treatment facility typically is a generally closed system of pipes, except at certain selected points, so as to inhibit dilution of the wastewater by runoff due to local rain showers or snow melt. The generally closed nature of the system is also intended to prevent any unwanted dispersal of the wastewater into the environment prior to proper treatment at the treatment facility.
Pretreatment facilities such as lift stations and pumping stations are typically included in the collection system at selected points to gather and pump wastewater to a next station and, ultimately, to a waste treatment plant. The pretreatment facilities typically include a large concrete pit with a number of incoming pipes carrying wastewater. A pump situated in the pit or wet well is coupled to an outflow pipe. The pump is generally controlled by switches that are responsive to the level of liquid in the pit. Generally, the pumps operate periodically, rather than continuously, with the level of wastewater in the pit falling during times that the pump is operating and rising when the pump is not operating. When the pumps are not operating and the wastewater is accumulating, there is more opportunity for the accumulation of significant populations of microbes that produce gases including hydrogen sulfide, methyl sulfide, methyl disulfide, mercaptans such as methyl mercaptan, ammonia, methylamines including di- and trimethylamine, various ethylamines and butylamines, pyridine, acetone, ketone, phenol, benzene, methane, butene, toluene, and many others, much of which is malodorous, noxious, and in some circumstances, dangerous to human health and welfare. The principal offensive gas present is generally hydrogen sulfide.
The frequent changes in liquid level in the wet wells of such pretreatment facilities requires the existence of vents that will permit entry of air into the pit as the wastewater level falls. As the level of wastewater rises, the gases that accumulate above the wastewater are often released out the same vents into the atmosphere. Since the wastewater lift stations, pumping stations, and other pretreatment facilities are sometimes situated in the immediate neighborhood of human habitations, the release of such gases can be much to the disgust of the local human inhabitants. The odors can be very strong especially if the accumulation period between pumping operations is long, or during summer when the temperatures are hot for extended periods thus encouraging the growth of microbial populations. The total prevention of gas release at such pretreatment facilities is generally not a realistic option. The treatment of such released gas so as to reduce its offensive character is a realistic option that has gained the attention of others previously.
It has been recognized that such noxious and malodorous gasses are treatable generally by an application of ozone as discussed, for example,. in Kobayashi, et al., U.S. Pat. No. 5,145,657 and Monagan, U.S. Pat. No. 5,601,786. A variety of equipment exists that can be used to generate ozone including, for example, Lowther, U.S. Pat. Nos. 3,954,586; 3,984,697; and 3,996,474; Schwab, et al., U.S. Pat. No. 4,110,086; Vaseen, U.S. Pat. No. 4,317,044; Weaver, U.S. Pat. Nos. 5,160,481; 5,173,268; and 5,751,007; and Kazi, et al., U.S. Pat. No. 5,578,280. Specifically, it has been previously suggested in Dickerson, U.S. Pat. Nos. 5,433,854 and 5,578,211, that such noxious and malodorous gasses might be eliminated from wastewater systems by an introduction of ozone into the system at various points together with the maintenance of a minimum level of nitrogen. It will be appreciated by those skilled in the art that the forced introduction of any gas within a closed space must result in either an elevated pressure within that space or the displacement of a like quantity of the same or another gas from that space through any available vent. As a practical matter, recognizing that no wastewater collection piping system is completely sealed, it has been found that the forced introduction of ozone into a wastewater collection piping system, as suggested by Dickerson, merely enhances the displacement of the noxious and malodorous gasses out of available vent points, much to the displeasure and potential harm of persons in the vicinity of the vents. Further, the introduction of the ozone into the system, at selected points such as lift stations and the like, must be very carefully controlled to avoid significant and substantial erosion of portions of the system by the highly oxidative ozone itself.
It has also been recognized that such noxious and malodorous gasses are treatable generally by withdrawing the gasses from the wet well and passing the gases through a bed of activated carbon. The carbon bed will operate satisfactorily for a period of time, however, periodically it must be replaced, and the spent carbon disposed of as required by law, typically at a hazardous waste facility. It has also been recognized that the replacement schedule for such carbon beds can be extended by exposing the activated carbon bed to a stream of ozone. Such equipment is available from Parson Environmental Products of Reading, Pennsylvania under the trademark carbOzone. This equipment is not satisfactory in that it is unable to eliminate odor xe2x80x9cspikesxe2x80x9d occurring during certain periods and requires the periodic disposal of the spent carbon. Furthermore, it is known that activated carbon and ozone can become unstable, and pose an explosion-fire hazard if ozone concentrations exceed 0.3%. Thus, the exposure of carbon beds to ozone should only occur under tightly controlled and monitored conditions that are generally not found in typical wastewater pretreatment facilities, which are generally unmanned facilities.
It is therefore desirable to construct a facility for treatment of gasses from wastewater lift stations, pumping stations, and other pretreatment facilities that will accommodate such odor xe2x80x9cspikesxe2x80x9d and does not require the disposal of any materials, particularly hazardous waste materials, does not pose an explosion-fire hazard, and emits no ozone into the atmosphere.
In accordance with the present invention, apparatus is connected to a vent of a wastewater pretreatment facility including a gas suction apparatus such as a fan or blower. The gas is withdrawn at a rate in excess of the gas production by microbes in the wastewater collection system so that the wet well of the wastewater pretreatment facility is maintained at a slight negative pressure. The gas withdrawn from the pretreatment facility is introduced by the fan or blower into a mixing chamber. An ozone generation apparatus is also coupled to the mixing chamber and provides a controlled supply of ozone, generally created electrically from the ambient air, to the mixing chamber. The ozone generation apparatus is adjusted to provide sufficient ozone to react with any noxious or malodorous components of the withdrawn gas even during peak production periods. A reaction conduit is coupled to the reaction chamber to receive the withdrawn gas and ozone. The reaction conduit is chosen to have surface features assuring turbulent flow of the gasses through the length of the conduit and to have sufficient length as to assure substantially complete decomposition and removal of the noxious or malodorous components from the withdrawn gas.
While the present invention has particular utility in connection with the reduction of odorous gasses from wastewater pretreatment facilities, the apparatus can be employed in similar fashion to treat a broad assortment of odorous gasses that may be present in a wide variety of facilities from which a controlled withdrawal of gas can be achieved, such as hog feeding enclosures and rendering plants. The invention includes the method of reducing the free release of odorous gasses by withdrawing the odorous gasses from an enclosed space at a controlled rate, mixing the withdrawn odorous gasses with a measured amount of ozone, and directing the mixed gases through a reaction conduit chosen to have surface features assuring turbulent flow of the gasses through the length of the conduit and to have sufficient length as to assure substantially complete decomposition and removal of the noxious or malodorous components from the withdrawn gas.
One desirable feature of the present invention is the specific provision of an reaction conduit that is designed to facilitate maximum mixing of the ozone and the withdrawn gasses to maximize their interaction. The reaction conduit is preferably constructed of an inexpensive and generally non-reactive material that is commonly available such as corrugated plastic pipe.
Another desirable feature of the present invention is the addition of an ozone sensor near an output of the reaction conduit to monitor the output to ensure that no overproduction of ozone is permitted, which might cause a free release of ozone into the environment. One or more additional sensors can be included at intermediate positions along the length of the reaction conduit to monitor the ozone level and, if appropriate, control the level of ozone produced by the ozone generation apparatus.
Still another desirable feature is a heated terminal reduction chamber located at the output of the reaction conduit that operates to reduce any residual ozone to ordinary oxygen prior to release into the atmosphere.
Still other features and advantages of the present invention will become apparent to those skilled in the art from a consideration of the following description of a preferred embodiment of the present invention illustrated in the accompanying figures.